Current air handler cabinets utilize many joints, fasteners, and compounds in their construction which create potential areas for air leakage and add costs in manufacturing. Additionally, known air handler units are typically constructed by securing a number of insulation panels to a framework to form a closed insulated cabinet. This also adds costs to manufacturing, and creates the potential for installation error. There is, therefore, a need for an insulated cabinet for air handler units that may be constructed without a framework and that will reduce the potential for air leakage.